1. Field of the Invention
The invention relates to an apparatus for contactless data and energy transmission and systems using the apparatus, the apparatus including a stationary part having an oscillator for contactless power transmission to a movable part with the aid of a pair of coils, the oscillation of the oscillator being split into a reference oscillation and an information oscillation, a phase displacement relative to the reference oscillation being forced or imposed upon the information oscillation as a function of the data to be transmitted, the phase-displaced oscillation being supplied through a first pair of coils and the reference oscillation being supplied through a second pair of coils to the movable part, in the movable part the transmitted oscillations being supplied to a demodulator circuit recovering the data from the phase displacement, and a data transmission from the movable part to the stationary part being provided by a load variation.
2. Description of the Related Art
Such an apparatus is described in German Patent DE-PS 34 47 560 C2, corresponding to U.S. Pat. No. 4,697,183, particularly in the description thereof pertaining to FIGS. 1 and 2. Such an apparatus is also known from an article in a publication known as Laboratory Report No. HTV 8902/HDP 8902, entitled "C2 Card" by Rainer Imjela of Philips Components, dated Oct. 11, 1989, which was published in German as Laborbericht C2-Card in January 1990 by Valvo/Philips Bauelemente, and particularly from FIG. 4 on page 27 thereof. Subcircuits of apparatuses of that generic type are described in German Patent DE-PS 31 49 789 C1, corresponding to Canadian Patent No. 1,183,927, German Patents DE-PS 32 21 356 C2, 32 25 039 C2, and 36 14 477 C2, the latter corresponding to U.S. Pat. No. 4,796,028, and German Published, Non-Prosecuted Application DE-OS 38 10 702 A1.
German Patent DE-PS 34 47 560 C2 describes an apparatus for contactless data and energy transmission, including a stationary part called a microstation, having an oscillator for contactless power transmission with the aid of at least one pair of coils, but typically with two pairs of coils to a movable part called the microunit. In the apparatus described therein, two coils are provided in the stationary part, which form a total of two pairs of coils with two coils in the movable part. The data transmission from the movable part to the stationary part is effected by simultaneous change of load at both coils of the movable part, which assures that proof of the change of load is possible at one of the two coils of the stationary part even if the combinations making up the coil pairs are transposed. The oscillation of the oscillator in the stationary part is split into two separate oscillations (a reference oscillation and an information oscillation). The first oscillation (information oscillation) is compelled to undergo a phase displacement relative to the other reference oscillation serving as a reference variable, as a function of the data to be transmitted. The out-of-phase oscillation is supplied to the movable part through one of the pairs of coils, and the other oscillation is supplied to it through the other pair of coils. The power transmission is effected with the aid of the two oscillations, through both pairs of coils. In the movable parts, the oscillations being transmitted are supplied to the demodulator in the form of a phase comparator, which recovers the data from the phase displacement.
The stationary unit described in German Patent DE-PS 34 47 560 C2 includes an oscillator having an output frequency which is furnished through respective flip-flops of different edge control, to two outputs. Therefore, two signals of the same frequency, which are in quadrature, are furnished. Those two signals are each connected to one coil, and each of the coils in the stationary part, together with one coil in the movable part, forms a coil pair. The phase position of the signal applied to one of the coils is displaceable by 180.degree.. As a result, the phase position can be switched back and forth by .+-.90.degree. between the two signals transmitted in the two coil pairs. The signal transmission from the stationary part to the movable part can thus be effected with the aid of 2 PSK (phase-shift keying, with two possible phase states). The movable part of the apparatus for contactless data and energy transmission, which is shown in the form of a block circuit diagram in FIG. 2 of German Patent DE-PS 34 47 560 C2, is essentially identical to the functional block circuit diagram of the movable part of an apparatus for contactless data and energy transmission shown on page 7 of the aforementioned German version of the C2 Card Laboratory Report. The signal is picked up at one of the connection terminals of each of the two coils present in the movable part and each is carried to one input of a demodulator circuit. The demodulator circuit passes on the signal sent by the stationary unit to subsequent circuit units. The demodulator circuit is followed by a circuit unit that defines the logic level of the signal at the turn-on instant of the movable part. Each time the movable part is turned on, a previously defined level, either high or low, is sent for a predetermined period of time for that purpose. When the movable part is turned on, the circuit part required for defining the level is reset, and then it defines the logic level of the movable part as a function of the predetermined sent signal. The two connection terminals of the two coils contained in the movable part are each followed by one rectifier. The output furnishing the positive voltage of one of the rectifiers is interconnected with the output furnishing the positive voltage of the other of the rectifiers, and the two output terminals each furnishing the negative voltage of the two rectifiers are also connected to one another. The common output of the two rectifier circuits is connected to both a variable load and a voltage regulator for furnishing the operating voltage of the movable part. The variable load is triggered in such a way that it primarily varies the real portion of the input impedance of the movable part of the apparatus for contactless data and energy transmission, as a function of the data to be transmitted from the movable part to the stationary part. Among other examples of a variable load is a synchronous switch which is open or closed as a function of the data to be transmitted and thus can connect a further impedance parallel to the input impedance of the movable part present in the open state of this switch. Given suitable triggering, the variable load acts as an amplitude modulator.
If the information oscillation is switched over between a +90.degree. and -90.degree. phase displacement, the oscillation amplitude at the coil of the stationary part being acted upon by the information oscillation moves toward zero at the instant of changeover, for a predetermined period of time. The energy supply of the movable part must be provided for this period of time by one pair of coils alone. If the coils of the movable part are capable of arbitrarily forming pairs of coils with the coils of the stationary part for the contactless data and energy transmission, then at least the coil of the stationary part transmitting the reference oscillation and both coils of the movable part, along with both rectifier configurations of the movable part, must be dimensioned in terms of their power capacity in such a way that they are suited for supplying all of the energy required by the movable part. The voltage regulator, for instance a series regulator, that follows the two rectifier circuits having outputs which are connected in parallel, must have a limit frequency that is higher than the data transmission rate of the amplitude modulator. It is only in this way that the jumps in potential, impressed by the amplitude modulator, at the input of the voltage regulator can be stabilized. It is therefore recommended that the voltage regulator that maintains the energy supply to the movable part have a limit frequency that is on the order of magnitude of the signal frequency of the oscillator in the stationary part, if the amplitude modulation is to superimpose a reliably detectable square signal upon the carrier frequency defined by the oscillator. Thus in such circuit configurations the data transmission rate from the movable part to the stationary part is defined by the limit frequency of the voltage regulator. At high data transmission rates, the voltage regulator is correspondingly expensive to manufacture.
At a given transmission characteristic for the signal transmission from the movable part to the stationary part, for example an amplitude rise in the movable part of 4 V, which is equivalent to a required load rise in the stationary part, a minimum allowable input voltage of the voltage regulator in the movable part that is increased by the amount of the amplitude rise is needed in order to furnish a required output voltage. In known contactless data and energy transmission apparatuses, the minimum allowable value of the voltage furnished by the coils at the input to the movable part must be higher than the required output voltage of the voltage regulator by an amount equal to the sum of the voltage dropping at the bridge rectifier, the minimum voltage dropping across the voltage regulator, and the amplitude rise. For instance, for an amplitude rise of 4 V, in order to obtain an output voltage of 5 V at the voltage regulator, the input voltage must typically be higher than 11 V. In monolithically integrated circuits, an integrated circuit that is supplied with an operating voltage of 5 V will accordingly also contain components having a breakdown voltage of over 11 V.
It is accordingly an object of the invention to provide an apparatus for contactless data and energy transmission and systems containing the apparatus, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, which are also suitable for higher data transmission rates, and in which the movable part does not require as high an input voltage as in known apparatuses in order to furnish a certain operating voltage to the movable part.